1. Field of the Invention
The present invention relates to an image processing apparatus, image processing method, and a program product for image processing, especially, image data correction, thereby to reproduce character images or the like clearly. More particularly, the present invention relates to an image processing apparatus, image processing method, and a program product for image processing capable of clearly reproducing character images against a halftone-dot region or a halftone solid region with a certain extent of density (these regions will be mentioned as background region hereinafter) clearly without white framed areas or turbid areas around character images against a background region.
2. Description of Related Art
In digital copiers that conduct image processing by reading images with a CCD sensor and resolving image data into pixels, edge enhancement processing is executed so as to reproduce characters and fine lines clearly. In edge enhancement processing, density of an inside portion of an edge (inner edge, hereinafter) is set higher than that of an original image, whereas density of an outside portion of the edge (outer edge, herein after) is set lower than that of the original image. Edge regions become distinctive with such edge enhancement processing, whereby characters and fine lines of an original document are reproduced clearly.
However, there has been a problem such that in case edge enhancement processing is applied to a character or the like against a background region, a white frame is formed around reproduced character image as shown in FIG. 28. To resolve the problem such as above, there has been taken a countermeasure. An example of resolution is disclosed in JP Laid-open Patent Publication No. 2000-307869. The Publication discloses a manner such that in case edge enhancement processing is applied to a character image against a halftone dot region or the like, the edge enhancement processing with respect to an outer edge region is not executed so as to avoid formation of a white frame around the character image.
However, technique disclosed in the Publication No. 2000-307869 has several problems such that (1) degree of clearness regarding a character image formed on a halftone dot region deteriorates, and (2) colors of an original image are reproduced turbidly. The problems as such occur because edge enhancement processing is not applied to an outer edge region. That is, smoothing processing is applied to the outer edge region as well as a halftone dot region beneath the edge region. As a result, the character image on the halftone dot region gets blurred and reproduced colors get turbid. Therefore, there has not been feasible to reproduce an image with high quality. Incidentally, same problems occur in case a character image laid out on a halftone solid region with a predetermined density is to be reproduced.